package com.juc.concurrency.jucExample.count;

import com.juc.concurrency.annoations.NotThreadSafe;
import lombok.extern.slf4j.Slf4j;

import java.util.concurrent.CountDownLatch;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Semaphore;

/**
 * 直接声明变量为volatile，计数的时候是线程不安全的
 */
@Slf4j
@NotThreadSafe
public class CountVolatileExample4 {

    // 请求总数
    public static int clientTotal = 5000;

    // 同时并发执行的线程数
    public static int threadTotal = 200;

    public static volatile int count = 0;

    public static void main(String[] args) throws Exception {
        ExecutorService executorService = Executors.newCachedThreadPool();
        final Semaphore semaphore = new Semaphore(threadTotal);
        final CountDownLatch countDownLatch = new CountDownLatch(clientTotal);
        for (int i = 0; i < clientTotal ; i++) {
            executorService.execute(() -> {
                try {
                    semaphore.acquire();
                    add();
                    semaphore.release();
                } catch (Exception e) {
                    log.error("exception", e);
                }
                countDownLatch.countDown();
            });
        }
        countDownLatch.await();
        executorService.shutdown();
        log.info("count:{}", count);
    }

    /**
     * 每次count++得到时候取出的都是主内存的值 但是线程依旧是不安全的
     */
    private static void add() {
        count++;
        // 1、count
        // 2、+1
        // 3、count 可能多个线程【同时】把+1后的结果写入到主存 所以count的值会变小
    }
}
